The invention relates to a pedal simulation device for simulating the reaction behavior of a pedal, in particular of a brake pedal of a vehicle brake system, comprising a cylinder, a piston disposed displaceably inside the cylinder and coupled to the pedal and delimiting a working chamber inside the cylinder, a resetting element capable of exerting a resetting force on the pedal, and a modeling device, which is fluidically connected to the working chamber, for influencing the reaction behavior of the pedal.
Such pedal simulation devices are already used in vehicles where an electrohydraulic brake system or an electromotive brake system is uncoupled from the brake force generation by means of a brake pedal. Such brake systems are referred to as “brake-by-wire” vehicle brake systems since the actual electrohydraulic or electromotive brake system that produces the braking effect is mechanically uncoupled from the brake pedal that initiates the braking operation. Rather, a brake pedal actuation is detected electronically by means of suitable sensors from various parameters, such as e.g., the actual brake pedal displacement or the force applied to the brake pedal as well as the brake pedal acceleration, and the respective brake system is controlled in accordance with the detected variables. In order nevertheless to convey to the driver of a motor vehicle a familiar mechanical brake pedal characteristic, whereby the brake pedal, upon actuation thereof, with increasing travel provides a growing resistance to further actuation and whereby the brake pedal in accordance with a hysteresis, upon release of the pedal, returns in a damped manner to its normal position, the pedal simulation devices of the initially described type are used.
Such a pedal simulation device is known, for example, from DE 100 39 670 A1. With this pedal simulation device, upon actuation of the brake pedal, the piston connected thereto by a connecting rod is displaced in the cylinder. In the process, gas is pressed by means of a throttle device out of a working chamber that is enclosed by the cylinder and the piston. With the aid of the throttle device it is possible to influence the discharge behaviour of the gas and hence the resistance that arises during a movement of the piston inside the cylinder. It has however emerged that the pedal simulation device according to this background art has a relatively sluggish response characteristic. The reason for this is that, because of the high compressibility of the gas, the piston may move a relatively long way inside the cylinder without a sufficiently high resistance that is perceptible by the driver of the motor vehicle being offered to this movement on account of the compression of the gas and the effect of the throttle. It is only after the piston has been displaced by a considerable distance that the pressure increase inside the cylinder is sufficient to generate a perceptible resistance to the pedal actuation. The driver accordingly has the unwanted impression that the brake system only becomes active relatively late.
From DE 197 55 481 C2 a pedal simulation device similar to the previously described background art is known. This device provides that, upon an actuation of the brake pedal, the gas enclosed between the piston and the cylinder may pass out of the working chamber in a substantially unimpeded manner through a non-return valve, wherein a resistance to the pedal movement is summoned up by means of a spring. During the resetting movement of the pedal, on the other hand, a throttle element, through which gas may pass in an inhibited manner into the working chamber enclosed by the piston and the cylinder, is effective so that a hysteresis is imposed on the movement of the brake pedal and the brake pedal may move under the action of the resetting spring in a damped manner into its normal position. However, the motional characteristic of this pedal simulation device differs widely from the desired behavior, especially because of the spring, which conveys to the driver a resistance to his pedal actuation that remains constant.
From EP 0 771 705 B1, moreover, a brake pedal simulation device is known, in which the piston moves in a cylinder that is closed at both ends, so that the piston delimits a working chamber at each end. Provided in the piston is a bore that enables an ex-change of gas between the two chambers inside the cylinder. Upon actuation of the brake pedal, the piston moves inside the cylinder, wherein gas from the one working chamber may flow through the piston into the other working chamber. This leads however to inadequate damping of the piston movement, so that the resulting brake pedal characteristic differs widely from the one to be conveyed to the driver.
Finally, from DE 196 38 102 C1 a vehicle hydraulic brake system is known, in which the basic idea of uncoupling of the brake pedal from the actual brake system is realized.